Infusion pumps currently present in the market consist of two basic types, syringe infusion pumps and volumetric infusion pumps. Typically, syringe infusion pumps accept a range of syringe sizes, typically from 1 cc to 60 cc or more in volume from a variety of syringe manufacturers. Typically these devices use a motor under control of a microprocessor. A motor such as is available from Maxon Precision Motors, Inc., Fall River, Mass., can be used. The motor is connected to a lead screw which advances a pushing element that pushes against the plunger of the syringe, driving it into the barrel of the syringe, thus dispensing fluid or other material. The devices have used sensors for determining the size of syringe loaded, the position of the plunger within its travel, whether the plunger is captured by the pushing element, and the driving force needed to push the plunger. The devices have also included encoders or other means for determining the motor speed.
The syringe drives have fixed the barrel of the syringe against a fixture, such as a V-block. A spring loaded clamp mechanism has been used to capture the barrel of the syringe against the V-block. Because the barrel diameter of a 1 cc syringe is significantly smaller than the barrel diameter of a 60 cc syringe, the pushing element has not always pushed along the center line of the syringe, and the variance between pushing element and syringe center line can be as much as 1 inch or more. The variance in the syringe center line with respect to the pushing surface has caused difficulties in measuring the force applied to the syringe which is used to estimate fluid pressure within the syringe. The variance has also caused inaccuracy in the resultant flow rate because the syringe plunger has not been driven into the syringe barrel squarely. Thus better schemes for mounting a syringe and driving its plunger are needed to eliminate these problems, and these schemes are provided by this patent application.